Surface science: physical chemistry of surfaces Massimiliano Bestetti Lesson N° October 2011

Nome relatore 2 Surface topography 1.Parameters 2.Measurements 3.Surface topography modification: examples 4.Standards

Nome relatore 3 Terminology and parameters

Nome relatore 4 Terminology and parameters Surface roughness parameters associated with irregularity properties in the profile length direction

Nome relatore 5 Terminology and parameters

Nome relatore 6 Terminology and parameters

Nome relatore 7 Terminology and parameters

Nome relatore 8 Terminology and parameters

Nome relatore 9 Terminology and parameters

Nome relatore 10 Terminology and parameters

Nome relatore 11 Terminology and parameters

Nome relatore 12 Terminology and parameters Surface roughness parameters associated with profile irregularity form

Nome relatore 13 Terminology and parameters Surface roughness parameters associated with profile irregularity form Kurtosis … For dental implants the primary rationale of surface roughness is to get an increased retention strength. Implant surface roughness is normally characterized by a number of surface parameters. There is no consensu as to which combination of roughness paramaters that best characterize the important topopgraphycal featurs of implant surface roughness...

Nome relatore 14 Terminology and parameters

Nome relatore 15 Terminology and parameters

Nome relatore 16 Terminology and parameters

Nome relatore 17 Terminology and parameters

Nome relatore 18 Terminology and parameters

Nome relatore 19 Terminology and parameters

Nome relatore 20 Terminology and parameters Numerical examples

Nome relatore 21 Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface Pressure-sensitive-adhesives (PSA) adhesive joint after a short contact time under a light pressure (vdW forces). Mechanical contact between. If the surface of the adhesive or that of the substrate are rough, this contact can be incomplete and evolve with contact time ( role of this incomplete contact on the subsequent debonding process). Air bubbles could be trapped at the interface between the adhesive and the surface and they could act as nucleating sites for cavities in the early stages of the failure process.

Nome relatore 22 Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface Pressure-sensitive-adhesives (PSA) ability to form bridging fibrils across the two surfaces, during the debonding stage. The fibrils are initiated by the formation of cavities at the interface between the adhesive and the hard surface or in the bulk of the adhesive. The role of the surface topography in the cavity nucleation process (changing the shape or length scale of the surface roughness) has been investigated in a systematic manner.

Nome relatore 23 Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface PSA poly (2-ethylhexyl acrylate) t ~ 100 µm Glass Stainless steel ( 5 mm) R a nm (5 levels) Temperature 23°C Nominal contact pressure 1 MPa Contact time 1 s Debonding rate 30 µm/s

Nome relatore 24 Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface Schematic of a nominal stress versus strain curve during the debonding stage. W adh is taken as the integral under the curve and represents the external work done for debonding. By measuring the contact area at the beginning of the pulloff stage (with the video camera) and the thickness of the adhesive layer, we can plot a nominal stress versus strain curve.

Nome relatore 25 Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface Steel ball surface roughness (WYKO optical profilometer used in vertical scanning interferometry mode (VSI) to map out the surface) R a, λ

Nome relatore 26 Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface R a, λ

Nome relatore 27 Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface A (Ra 11 nm)E (Ra 148 nm)

Nome relatore 28 Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface A (Ra 11 nm)E (Ra 148 nm) Wadh decreases with increasing roughness, from about 25 J/m 2 for A to 15 J/m 2 for E. Ra (nm)

Nome relatore 29 Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface A (Ra 11 nm)E (Ra 148 nm)

Nome relatore 30 Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface A (Ra 11 nm)E (Ra 148 nm)

Nome relatore 31 Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface A (Ra 11 nm)E (Ra 148 nm)

Nome relatore 32 Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface Dependence of σ max on the characteristic amplitude of the grooves made by the polishing wheels on the steel surfaces. Since the maximum in stress is due to the nucleation of cavities, the grooves undoubtedly play an essential role in the level of stress at which a cavity can nucleate in the adhesive layer. The role of surface roughness is to create weak spots under residual tension which will therefore allow cavity growth at a lower level of nominal stress. The presence of deeper grooves can: – increase the size of air pockets trapped during the contact stage; – alter the stress distribution near the surface in such a way that more spots are under residual tension stresses. The second effect of the presence of topographical asperities is the slowing down of the propagation of these cavities along the surface ( the propagation of the crack front may be more dissipative ).